Related question: Is there an amp power formula?

When I look at amps in a shop or online, I ask myself what the amp is suitable for:

• Can it be played quietly enough for home use without disturbing the neighbours/sleeping wife/etc.?
• Is it loud enough to play along with acoustic instruments?
• Is it loud enough to be heard by an audience in a room of a certain size?
• Is it loud enough to be heard alongside a drumkit
• etc.

It's clear that wattage isn't an adequate indicator: the Beatles played gigs on Vox AC15s -- I have owned a 15 watt guitar amp that couldn't possibly be heard over a drumkit.

It's also clear that size isn't much of an indicator either -- there are tiny guitar amps that are seriously loud.

When choosing an amp, how do I know how loud it's going to be?

Quick word on scope:

• Let's not talk about micing up amps for the PA.
• Let's be general and talk about bass, guitar, keyboard amps, and amps for any other electric instrument.

Related question: Is there an amp power formula?

When I look at amps in a shop or online, I ask myself what the amp is suitable for:

• Can it be played quietly enough for home use without disturbing the neighbours/sleeping wife/etc.?
• Is it loud enough to play along with acoustic instruments?
• Is it loud enough to be heard by an audience in a room of a certain size?
• Is it loud enough to be heard alongside a drumkit
• etc.

It's clear that wattage isn't an adequate indicator: the Beatles played gigs on Vox AC15s -- I have owned a 15 watt guitar amp that couldn't possibly be heard over a drumkit.

It's also clear that size isn't much of an indicator either -- there are tiny guitar amps that are seriously loud.

When choosing an amp, how do I know how loud it's going to be?

Quick word on scope:

• Let's not talk about micing up amps for the PA.
• Let's be general and talk about bass, guitar, keyboard amps, and amps for any other electric instrument.